During some test in local play, I found MK17 has some serious bug. We all know that MK17 is the only battle rifle needs 2 shots to kill a guy, but it's not always the case. I found that when you shoot the enemy through arms to the chest, it's always one hit kill, but when you directly hit chest, it needs 2 shots. Pic below.
So the bullet goes through arms to chest lead to one shot kill but a direct hit on the chest will not, hope devs can notice it, thanks
UPDATE: The bullet is also one hit kill when enemy at prone stance. (To the chest)